Polyalpha-olefins (PAOs) comprise a class of hydrocarbons typically manufactured by the catalytic oligomerization (polymerization to low-molecular-weight products) of linear alpha-olefin (LAO) monomers. These typically range from 1-octene to 1-dodecene, with 1-decene being a suitable material, although oligomeric copolymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins. PAO products have achieved importance in the lubricating oil market. Typically there are two classes of synthetic hydrocarbon fluids (SHF) produced from linear alpha-olefins, the two classes of SHF being denoted as PAO and HVI-PAO (high viscosity index PAOs). PAOs and HVI-PAOs of different viscosity grades are typically produced using promoted BF3 or AlCl3 catalysts. Subsequent to polymerization, the PAO lubricant range products are typically hydrogenated in order to reduce the residual unsaturation, generally to a level of greater than 90%.
Synthetic PAOs have found wide acceptability and commercial success in the lubricant field for their superiority to mineral based lubricants. In terms of lubricant property improvement, industrial research efforts on synthetic lubricants have led to PAO fluids exhibiting useful viscosities over a wide range of temperature, i.e., improved viscosity index, while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil. These relatively new synthetic lubricants lower mechanical friction, enhancing mechanical efficiency over the full spectrum of mechanical loads and do so over a wider range of operating conditions than mineral oil lubricants. Polyalpha-olefins of different viscosity grades are known to be useful in synthetic and semi-synthetic lubricants and grease formulations. See, for instance, Chapters 19 to 27 in Rudnick et al., “Synthetic Lubricants and High-Performance Functional Fluids”, 2nd Ed. Marcel Dekker, Inc., N.Y. (1999). Compared to the conventional mineral oil-based products, these PAO-based products have excellent viscometrics, high and low temperature performance. They usually provide energy efficiency and extended service life.
HVI-PAOs are characterized by having a high viscosity index (VI) of about 130 and above, more preferably 150 and above, still more preferably 160 and above, yet still more preferably 200 and above, and one or more of the following characteristics: a branch ratio of less than 0.19, a weight average molecular weight of between 300 and 45,000, a number average molecular weight of between 300 and 18,000, a molecular weight distribution of between 1 and 5, and pour point below −15° C. Measured in carbon number, these molecules range from C30 to C1300. Viscosities of the HVI-PAO oligomers measured at 100° C. range from 3 centistokes (“cSt”) to 15,000 cSt. These HVI-PAOs have been used as basestocks in engine and industrial lubricant formulations.
In the production of PAOs and HVI-PAOs, the feed is usually limited to one specific alpha-olefins, usually 1-decene. Occasionally, when 1-decene is not available in large enough quantity, small to moderate amounts of 1-octene or 1-dodecene is added to make up the quantity. It is generally thought that 1-decene is the most preferred feed (see reference “Wide-Temperature Range Synthetic Hydrocarbon Fluids” by J. A. Brennen, Ind. Eng. Chem. Prod. Res. Dev., 19, 2-6 (1980). When mixtures of feed are used, the products tend to be blocky copolymers rather than random copolymers and/or products produced at the beginning of the process are different than that produced at the end of the process, and the inhomogeneous polymer product will be characterized by poor viscosity indices (VI) and poor low temperature properties are produced. Thus, in the past, PAOs and HVI-PAOs have generally been made using pure C10 feeds.
Efforts have been made to prepare various PAOs using metallocene catalyst systems where PAOs are produced from meso-forms of certain metallocene catalysts under high hydrogen pressure. The use of rac-ethyl-bis(indenyl) zirconium dichloride or rac-dimethylsilyl-bis(2-methyl-indenyl) zirconium dichloride in combination with MAO at 40° C. (at 200 psi hydrogen or 1 mole of hydrogen) to produce isotactic polydecene have also been reported. Others have made various PAOs, such as polydecene, using various metallocene catalysts not typically known to produce polymers or oligomers with any specific tacticity.
To date however, PAOs made with metallocenes have not found wide applicability in the marketplace, particularly the lubricant marketplace, due to inefficient process, cost and property deficits. Accordingly, there exists a need in the art for providing PAOs and or HVI-PAOs and an improved process to produce them. There is a need in the art for new and improved catalysts and catalyst systems to obtain new and improved PAOs, polymerization processes, and the like. Accordingly, there is a need in the art for new and improved catalyst systems for the polymerization of olefins, in order to achieve specific properties.